Method of separating the heart and sap wood constituents of coniferous woods



DEC. 17, v QS 2,225,459

METHOD OF SEPARATING THE HEART AND SAP WOOD CONSTITUENTS OF CONIFEROUS WOODS Filed July 29, 1939 2 Sheets-Sheet l INVENTOR 9:1/7 e 2/; fuse ATTORN EY5 Dec. 17, 1940. G. v. PALMROSE 2,225,459

METHOD OF SEPARATING THE HEART AND SAP WOOD CONSTITUENTS OF CONIFEROUS WOODS Filed y 29, 3 2 Sheef s-Sheet 2 INVENTOR 9 7a /01 mug ATTORNEYS Patented Dec. 17, 1940 PATENT orrica METHOD OF SEPARATING THE AND SAP WOOD CONSTITUENTS F CONIF- mtoUs woons George V. Palmrose, Long-view, Wash., assignor,

by direct and mesne asaignments, toweyerhaeuser Timber Company, Longview, Wasln, a. corporation of Washington Application July 29, 1935, Serial No. 287,282

8 Claims.

This invention relates to the separation of the heart and sap wood constituentsof coniferous woods, and particularly to the preparation of such materials for pulping.

There are a number of species of coniferous woods which are not readily reduced to cellulose by the sulphite process. Attempts to treat such woods usually result in non-uniform pulp and a high percentage of screenings. Examination of the screenings discloses that they consist mostly ofheart wood which is not readily amendable to treatment by the sulphite process. Examination of thepulp indicates that a portion of the wood has been over-cooked, whereas anotherportion is under-cooked, so that the pulp is of little value. It requires usually a very high proportion of chlorine to bleach it to a satisfactory whiteness, and the eventual product is unsatisfactory.

Some attempt has been made heretofore to avoid this difllcultyby the selection of relatively immature trees in which the sap wood predomicontain a larger proportion of heart wood, de-

pending upon growth, soiland climatic conditions, and it is practically impossible to select trees for treatment on the basis of age, so as to avoid the difllculties hereinbefore mentioned.

It is the object of the present invention to afford a simple and satisfactory method of separating the heart from the sap wood after the material has been reduced to chips, thus permitting selection of the sap wood for treatment by the sulphite process. The separated heart woodcan be treated satisfactorily by the kraft or sulphate process, to produce pulp of the desired quality, so that all the wood can be utilized successfully.

Other objects and advantages of the invention will be apparent as it is better understood by reference to the following specification, in which the preferred embodiments of the invention are described in connection with the drawings, in which a Fig. 1 is a diagrammaticview of an apparatus adapted for use in the practice of the invention; and

Fig. 2 is a similar view illustrating an alternative structure adapted to be similarly employed.

The sap wood, of all species of coniferous woods, is more open in its structure and is provided with continuous passages communicating from fiber to fiber, which are readily permeated by air and moisture. The heart wood, on the other hand, represents wood which is no longer growing, and the passages are either partially or whereas the heart wood treated in the same mann'er does not'become filled with water and consequently has a lower specific gravity due to the entrapped air. in the closed passages. This phenomenon affords a practical basis for separating the heart wood from the sap wood, since after treatment the heart wood floats on water, whereas the sap wood sinks.

The permeation of the sap wood with water may be accomplished in a variety of ways, two of the most practicable being hereinafter described. In one method. the chips are subjected in any suitable manner to a vacuum sufficient to withdraw air from the open passages in the sap wood. After the vacuum treatment, the chips are submerged in water which replaces the air withdrawn from the passages, causing the sap wood to become heavier. The heart wood is not affected appreciably bythis treatment, and the chips which consist principally of heart wood float on the water, whereas the sap woodchips sink. Mechanical means of any suitable type may be employed then to separate the two constituents.

As an alternative procedure, the air in the sap wood chips may be driven off by heating the chips to a suitable temperature, for example about 212 F. Any suitable heating arrangement may be employed, but I prefer to introduce steam in quantity sufiicient to raise the temperature of the chips to approximately the temperature in- In describing the operation in more detail, I

shall refer to typical equipment illustrated in the accompanying drawings. It is to be understood, however, that numerous variations in the details of equipment are possible, and that the invention is not limited to any particular type of equipment or to details of procedure. The essential a suitable vessel, preferably cylindrical and constructed of steel or other suitable material to withstand a vacuum of about 28 inches of mercury. Connected to the bottom of the vessel 5 is a pipe 6 of large diameter and not less than 30 feet in length. The vessel 8 is provided with anopening at its top adapted to be sealed by a vacuum-tight closure I. A valve, for example a perforated plug 8. is provided in the opening at the juncture of the vessel! and the pipe 6, to permit the passage of water, but retaining the chips in the vessel 5, The plug 8 may be connected by a chain 8 to the upper part of the receptacle 5 to facilitate manipulation.

The end of the pipe 6 extends into a tank It and the valve 22, adapted to be swung from'the full line position to that shown in dotted lines by any suitable mechanical means, is provided at the bottom of the pipe 6 to close or open the outlet to the tank It during the operation. A suitable pump ll connected by a pipe I2 to a source of water supply is provided with a discharge outlet l3 having a valve 14, so that water may be delivered as desired into the pipe 8.

A suitable conveyor it permits delivery of the chips'to the opening at the top of the vessel 8. In the bottom of the tank III a conveyor I6 is adapted to deliver the chips which sink to the bottom of the tank to a sump ll, from which the chips are removed by a conveyor is. A conveyor l9'is adapted to withdraw chips from the surface of the water in the tank Hi and to deliver them to a trough 20 from which they are withdrawn by a conveyor 2!. It is to be understood that the several conveyors are actuated by suitable mechanical devices, not shown since they are well known in the art.

In the operation of the method, in apparatus such as that described, the vessel 6 is first filled with chips consisting of heart and sap wood. The chips are prevented from falling into the pipe 8 by the plug 8. The valve 22 is closed and the valve is is opened. and the pump II is then actuated to supply water to the pipe 0. The water eventually rises until all of the chips are submerged and the vessel 5 is filled. The closure 1 is then secured, the valve I4 is closed, and the valve 22 is opened. The column of water falls to a point where it is supported by atmospheric pressure and induces a vacuum in the receptacle 5 of from 26 to 28 inches of mercury. The vacuum need be maintained only for a period of approximately 2 to 5 minutes in order to withdraw the air from the chips of sap wood. The valve 22 is. then closed, the valve I4 is opened, and the pump,

is started to force the water again to rise in the vessel 5 until the vessel is full. The closure I is then opened and the plug 8 is raised, permitting the chips to descend into the pipe 6. The valve 22 is then opened, permitting the mass of water and chips to flow into the tank Ill. Here the chips of sap wood which have become saturated with water sink to the bottom of the tank, whereas the heart wood chips float. The chips of sap wood and heart wood are withdrawn respectively by the conveyors I6 and I8 and discharged from the apparatus. The sap wood chips may be dethis apparatus, a column 22 of suitable height is provided to receive chips supplied continuously by conveyor 24. The operation is continuous, the chips moving gradually down the column 23, in which they are subjected to the effect of steam supplied through a plurality of pipes 25 having valves 26. Asthe chips descend, they are heated to approximately 212 F., and air trapped in the open passages of the sap wood is driven oil, The chips eventually descend to the bottom of the column and are picked up by a conveyor 21 which delivers the chips to a tank 28 filled with water. The water immediately fills the passages in the sap wood from which air has been driven off. It cannot, however, enter the closed passages of the heart wood, and consequently the heart wood floats, whereas the sap wood sinks. The sap wood is withdrawn from the bottom of the tank 28 by a conveyor 29 which delivers it to storage for treatment by the sulphite process. The heart wood is taken on by a conveyor 30 from the surface of the water in the tank 28, and delivered to storage for treatment by an alkaline pulping process.

The method as conducted in the apparatus shown in Fig. 1 is intermittent, whereas in the apparatus shown in Fig. 2 it is continuous. The adoption and use of one or the other of these procedures will dependupon existing-economic conditions. Where an adequate quantity of exhaust steam is available and inexpensive, it will be found most economical to operate in the apparatus shown in Fig. 2. Where the cost of steam is high, the vacuum-system as illustrated in Fig. 1 is more economical. Either procedure results in the efficient separation of sap wood from heart wood and permits the manufacture of high grade sulphite pulp from species of coniferous woods which ordinarily cannot be treated successfully by the sulphite process. Since the constituents of the wood after separation are each available for separate treatment by processes to which they are suited, it is possible to recover all of the available material in the form of satisfactory pulp.

Various changes may be 'made in the procedure and in the apparatus employed without departing from the invention or sacrificing any of its 'advantages.

I claim:

1. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, treating a mixed mass of the heart wood and sap wood chips to increase the apparent specific gravity of the sap wood chips relative to the apparent specific gravity of the heart wood chips, and eflecting separation of the heart wood and sap wood chips lay the diflerence in their apparent specific gravi- 2. In the method of preparing coniferous 7o woods for pulping. the improvement which comand replacing it with water to thereby increase their apparent specific gravity relative to the apparent specific gravity of the heart wood chips, and effecting separation of the heart wood and sap wood chips by the difference in their specific gravities. V

3. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, removing air from the cells of the sap wood chips and replacing it with water to thereby increase their apparent specific gravity relative to the apparent specific gravity of the heart wood chips, and effecting separation of the heart wood chips from the sap wood chips by floating the heart wood chips in an aqueous medium in which the sap wood chips sink.

4. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, subjecting a mixed mass of the heart wood and sap wood chips to a partial vacuum for a length of time sufficient to extract air from the cells of the sap wood chips, thereafter maintaining the mass of chips in a body of water for a length of time sufficient for water to permeate the evacuated cells of the sap wood chips and hereby increase their apparent specific gravity relative to the apparent specific gravity of th heart wood chips, and effecting separation of the heart wood and sap wood chips by the difference in their apparent specific gravities.

5. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, subjecting a mixed mass of the heart wood and sap wood 40 chips in a closed chamber to a partial vacuum induced by the weight of a column of water for a length of time sufiicient to extract air from the cells of the sap wood chips, thereafter immediately flooding the chips with water until'the water 45 fills the evacuated cells in the sap wood chips and increases their apparent specific gravity relative to the apparent specific gravity of the heart wood chips, and effecting separation of the heart and sap wood chips by the difference in their apparent specific gravities.

6. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, heating a mixed mass of the heart wood and sap wood chips for a length of time sufilcient to expel air from the sap wood chips, and thereafter immediately quenching the mass of chips in water, whereby the sap wood chips absorb excess water and have their apparent specific gravity increased relative to the apparent specific gravity of the heart wood chipsand sink while the heart wood chips float.

7. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, heating a mixed mass of the heart wood and sap wood chips with steam for a length of time sufilcient to expel air from the sap wood chips, and thereafter immediately quenching the mass of chips in water, wherby the sap wood chips absorb excess water and have their apparent specific gravity increased relative to the apparent specific gravity of the heart wood chips and sink while the heart wood chips float.

8. In the method of preparing coniferous woods for pulping, the improvement which comprises reducing both the heart wood and the sap wood of a piece of coniferous wood to chips, heating a mixed mass of the heart wood and sap wood chips with steam at approximately 212 F. for a length of time sufficient to expel air from the sap wood chips, and thereafter immediately quenching the mass of chips in water, whereby the sap wood chips absorb excess water and have their apparent specific gravity increased relative to the apparent specific gravity of the heart wood chips and sink while the heart wood chips float.

GEORGE V. PALMROSE. 

